1. Field of the Invention
The present invention relates generally to improvements of a tape cassette for holding a magnetic tape within a cassette case. More particularly this invention relates to an upper half and a lower half which constitute a tape cassette and a tape guide member.
2. Description of the Prior Art
A conventional magnetic tape cassette is assembled in such a manner that an upper cassette half and a lower cassette half, each being molded from plastic material and approximately same in shape, are put together and fixed by screws. The magnetic tape cassette is provided through its front side wall with a plurality of opening portions through which a magnetic head, a pinch roller and the like of a tape recorder and so on are inserted thereinto. At predetermined positions near the inside of the opening portions, there are provided a tape guide pin, a tape guide member, a tape guide roller and a tape pad mechanism supported by a shield plate. Further, a magnetic tape wound around reels is held inside the cassette case so as to be transported along the tape guide member.
By the way, among the causes which will deteriorate the tone quality of a cassette tape recorder, as the cause owing to the tape cassette itself, there may be considered those from the tape guide system and the cassette half (cassette case) system.
In the cassette half system, since the whole thereof is molded from plastics, the cassette halves are apt to be deformed by distortion. And, since the deformed cassette case holds as it is therein the magnetic tape, poor transportation, track displacement, phase deviation and the like occur. As the causes why such distortion occurs in the cassette halves, there may be exemplified such causes that the shape of the cassette halves are quite complicated and in addition, the plastics forming the cassette halves are deformed by heat and stress.
On the other hand, in the tape guide system, in the inside of the cassette halves, there are provided a tape guide block (a collective member formed of a plurality of tape guide members) which faces to and exists near the front opening portion, tape guide pins and tape guide rollers formed at both sides of the tape guide block. Among those, the portion or member which most influences the tape running and recording and/or reproducing is the above tape guide block. The tape guide block member is formed integral with the cassette half from the plastic molding. The surface of the tape guide block member which contacts with the magnetic tape must be formed accurately vertical. However, since in order to facilitate the extraction of the cassette half from the metallic mold, a draft inclination is provided on the metallic mold, the tape guide surface is inevitably inclined a little. As a result, the tape guide surface can not be formed as the accurately vertical surface so that the magnetic tape can not be transported along the accurate straight line.
Moreover, the surface roughness of the tape guide block member is determined by the good or bad of the surface finishing of the metallic mold and the scar and deformation formed on the surface of the tape guide block member when the cassette half is drafted from the metallic mold. Accordingly, the friction state between the tape guide block member and the magnetic tape is changed thereby to cause the tone quality of individual tape cassettes to be scattered. Furthermore, since the above tape guide block member is made of plastic material, the shearing and the heat are caused by the sliding friction between the tape guide block member and the magnetic tape (which is normally provided by coating a magnetic paint on a film made of polyester resin) so that the magnetic tape is slackened. In addition, since the tape guide block member is provided only at one cassette half and guides the magnetic tape being transported, due to the contact force caused from the magnetic tape to the tape guide block member by the tape tension, the tape guide block member is easily distorted and this distortion is cooperated with the fluctuation of the tape tension to thereby cause the distorting vibration in the tape guide block member.